Rise of oceanographic barriers in continuous populations of a cetacean: the genetic structure of harbour porpoises in Old World waters

Background

Understanding the role of seascape in shaping genetic and demographic population structure is highly challenging for marine pelagic species such as cetaceans for which there is generally little evidence of what could effectively restrict their dispersal. In the present work, we applied a combination of recent individual-based landscape genetic approaches to investigate the population genetic structure of a highly mobile extensive range cetacean, the harbour porpoise in the eastern North Atlantic, with regards to oceanographic characteristics that could constrain its dispersal.

Results

Analyses of 10 microsatellite loci for 752 individuals revealed that most of the sampled range in the eastern North Atlantic behaves as a 'continuous' population that widely extends over thousands of kilometres with significant isolation by distance (IBD). However, strong barriers to gene flow were detected in the south-eastern part of the range. These barriers coincided with profound changes in environmental characteristics and isolated, on a relatively small scale, porpoises from Iberian waters and on a larger scale porpoises from the Black Sea.

Conclusion

The presence of these barriers to gene flow that coincide with profound changes in oceanographic features, together with the spatial variation in IBD strength, provide for the first time strong evidence that physical processes have a major impact on the demographic and genetic structure of a cetacean. This genetic pattern further suggests habitat-related fragmentation of the porpoise range that is likely to intensify with predicted surface ocean warming.     

Adverse effects of conjugated alpha-linolenic acids (CLnA) on lipoprotein profile on experimental atherosclerosis in hamsters

Conjugated linoleic acids (CLAs) such as rumenic acid (RA) have the potential to alter blood lipid profiles in animals and in humans. In contrast, physiological effects of conjugated α-linolenic acids (CLnAs), which concomitantly are omega-3 and conjugated fatty acids, are still unknown. The aim of this study was to evaluate the potential of CLnA to interfere in early steps of atherosclerosis by altering lipoprotein profiles and fatty streaks in the aortas. F1B hamsters were fed a control or one of the three hypercholesterolemic (HC) diets: HC-control, HC-RA (18:2 cis-9, trans-11) or HC-CLnA (CLnA: equimolar mixture of 18:3 cis-9, trans-11, cis-15 and cis-9, trans-13, cis-15) diet. In low-cholesterol control-fed hamsters, the proportion of high-density lipoprotein cholesterol (HDL-C) was around 45% while in HC-fed hamsters, HDL-C was around 10% and cholesterol was mostly (80%) carried by triglyceride-rich lipoproteins (TRL). Low-density lipoprotein (LDL) triglycerides (TGs) increased by approximately 60% in hamsters fed either HC-RA or HC-CLnA compared with HC-controls but not compared with the low-cholesterol control diet. HDL cholesterol decreased by 24% and 16% in hamsters fed HC-RA and HC-CLnA, respectively. Small dense LDL-cholesterol increased by approximately 60% in hamsters fed HC-RA and HC-CLnA compared with the HC-control group and by more than a 100% compared with hamsters on the control diet. The relative percentage of liver cholesteryl ester content increased by 88% in hamsters fed HC diets compared with the control diet. Significant differences in fatty streaks were observed between control and HC-diet-fed hamsters. However, no significant difference was observed among the HC-diet-fed hamsters. This study shows that animals fed any one of the HC diets developed an adverse lipoprotein profile compared with a normolipidic diet. Also, HC-RA or HC-CLnA diets altered lipoprotein profile compared with animals fed the HC-control diet but had no beneficial effects on atherosclerosis.     

Carbon consequences of drought differ in forests that resprout

Prolonged drought and intense heat‐related events trigger sudden forest die‐off events and have now been reported from all forested continents. Such die‐offs are concerning given that drought and heatwave events are forecast to increase in severity and duration as climate change progresses. Quantifying consequences to carbon dynamics and storage from die‐off events are critical for determining the current and future mitigation potential of forests. We took stand measurements five times over 2+ years from affected and unaffected plots across the Northern Jarrah Forest, southwestern Australia, following an acute drought/heatwave in 2011. We found a significant loss of live standing carbon (49.3 t ha^?1), and subsequently a significant increase in the dead standing carbon pool by 6 months post‐die‐off. Of the persisting live trees, 38% experienced partial mortality contributing to the rapid regrowth and replenishment (82%–88%) of labile carbon pools (foliage, twigs, and branches) within 26 months. Such regrowth was not substantial in terms of net carbon changes within the timeframe of the study but does reflect the resprouting resilience of this forest type. Dead carbon generated by the die‐off may persist for centuries given low fragmentation and decay rates resulting in low biogenic emission rates relative to other forest types. However, future fire may threaten persistence of both dead and live pools via combustion and mortality of live tissue and impaired regrowth capacity. Resprouting forests are commonly regarded as resilient systems, however, a changing climate could see vulnerable portions of forests become carbon sources rather than carbon sinks.     

Changes in structure of over‐ and midstory tree species in a Mediterranean‐type forest after an extreme drought‐associated heatwave

Worldwide, extreme climatic events such as drought and heatwaves are associated with forest mortality. However, the precise drivers of tree mortality at individual and stand levels vary considerably, with substantial gaps in knowledge across studies in biomes and continents. In 2010–2011, a drought‐associated heatwave occurred in south‐western Australia and drove sudden and rapid forest canopy collapse. Working in the Northern Jarrah (Eucalyptus marginata) Forest, we quantified the response of key overstory (E. marginata, Corymbia calophylla) and midstory (Banksia grandis, Allocasuarina fraseriana) tree species to the extreme climate event. Using transects spanning a gradient of drought impacts (minimal (50–100 m), transitional (100–150 m) and severe (30–60 m)), tree species mortality in relation to stand characteristics (stand basal area and stem density) and edaphic factors (soil depth) was determined. We show differential mortality between the two overstory species and the two midstory species corresponding to the drought‐associated heatwave. The dominant overstory species, E. marginata, had significantly higher mortality (~19%) than C. calophylla (~7%) in the severe zone. The midstory species, B. grandis, demonstrated substantially higher mortality (~59%) than A. fraseriana (~4%) in the transitional zone. Banksia grandis exhibited a substantial shift in structure in response to the drought‐associated heatwave in relation to tree size, basal area and soil depth. This study illustrates the role of climate extremes in driving ecosystem change and highlights the critical need to identify and quantify the resulting impact to help predict future forest die‐off events and to underpin forest management and conservation.     

Population structure,connectivity, and demographic history of an apex marine predator,the bull shark Carcharhinus leucas

Knowledge of population structure, connectivity, and effective population size remains limited for many marine apex predators, including the bull shark Carcharhinus leucas. This large‐bodied coastal shark is distributed worldwide in warm temperate and tropical waters, and uses estuaries and rivers as nurseries. As an apex predator, the bull shark likely plays a vital ecological role within marine food webs, but is at risk due to inshore habitat degradation and various fishing pressures. We investigated the bull shark's global population structure and demographic history by analyzing the genetic diversity of 370 individuals from 11 different locations using 25 microsatellite loci and three mitochondrial genes (CR, nd4, and cytb). Both types of markers revealed clustering between sharks from the Western Atlantic and those from the Western Pacific and the Western Indian Ocean, with no contemporary gene flow. Microsatellite data suggested low differentiation between the Western Indian Ocean and the Western Pacific, but substantial differentiation was found using mitochondrial DNA. Integrating information from both types of markers and using Bayesian computation with a random forest procedure (ABC‐RF), this discordance was found to be due to a complete lack of contemporary gene flow. High genetic connectivity was found both within the Western Indian Ocean and within the Western Pacific. In conclusion, these results suggest important structuring of bull shark populations globally with important gene flow occurring along coastlines, highlighting the need for management and conservation plans on regional scales rather than oceanic basin scale.     

Metabolite pools of the reef building coral Montipora capitata are unaffected by Symbiodiniaceae community composition

Some reef corals form stable, dominant or codominant associations with multiple endosymbiotic dinoflagellate species (family Symbiodiniaceae). Given the immense genetic and physiological diversity within this family, Symbiodiniaceae community composition has the potential to impact the nutritional physiology and fitness of the cnidarian host and all associated symbionts. Here we assessed the impact of the symbiont community composition on the metabolome of the coral Montipora capitata in Kāne‘ohe Bay, Hawai‘i, where different colonies can be dominated by stress-tolerant Durusdinium glynnii or stress-sensitive Cladocopium spp. Based on our existing knowledge of these symbiont taxa, we hypothesised that the metabolite profile of D. glynnii-dominated corals would be consistent with poorer nutritional support of the host relative to those corals dominated by Cladocopium spp. However, comparative metabolite profiling revealed that the metabolite pools of the host and symbiont were unaffected by differences in the abundance of the two symbionts within the community. The abundance of the individual metabolites was the same in the host and in the endosymbiont regardless of whether the host was populated with D. glynnii or Cladocopium spp. These results suggest that coral-dinoflagellate symbioses have the potential to undergo physiological adjustments over time to accommodate differences in their resident symbionts. Such mechanisms may involve host heterotrophic compensation (increasing the level of nutrition generated by feeding relative to delivery from the algae), dynamic regulation of metabolic pathways when exchange of metabolites between the organisms differs, and/or modification of both the type and quantity of metabolites that are exchanged. We discuss these adjustments and the implications for the physiology and survival of reef corals under changing environmental regimes.

     

Evolving maps in craniofacial development

The shaping of the vertebrate head results from highly dynamic integrated processes involving the growth and exchange of signals between the ectoderm, the endoderm, the mesoderm and Cephalic Neural Crest Cells (CNCCs). During embryonic development, these tissues change their shape and relative position rapidly and come transiently in contact with each other. Molecular signals exchanged in restricted regions of tissue interaction are crucial in providing positional identity to the mesenchymes which will form the different skeletal and muscular components of the head. Slight spatio-temporal modifications of these signalling maps can result in profound changes in craniofacial development and might have contributed to the evolution of facial diversity. Abnormal signalling patterns could also be at the origin of congenital craniofacial malformations. This review brings into perspective recent work on spatial and temporal aspects of facial morphogenesis with particular focus on the molecular mechanisms of jaw specification.